<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../vue.js"></script>
</head>
<body>
    <div id="app">
        ￥: <input v-model="yuan" type="text"> <br>
        $: <input v-model="dollar" type="text"><br>
        {{yuan+'人民币='+dollar+'美元'}}
    </div>
</body>
<script>
    var app = new Vue({
        el:'#app',
        data() {
            return {
                yuan:0,
                dollar:0,
            }
        },
        watch: {
            yuan:function (newValue) {
                this.dollar=newValue*5
            },
            dollar:function (newValue) {
                this.yuan=newValue*0.2
            }
        },
    })
</script>
</html>